content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
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  // modification, are permitted provided that the following conditions are
  // met:
  //
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  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
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  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  import java.io.ByteArrayInputStream;
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InvalidObjectException;
  import java.io.ObjectInputStream;
  import java.io.OutputStream;
  import java.io.Serializable;
  import java.io.UnsupportedEncodingException;
  import java.nio.ByteBuffer;
  import java.nio.charset.Charset;
  import java.nio.charset.UnsupportedCharsetException;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.List;
  import java.util.NoSuchElementException;
  
  /**
   * Immutable sequence of bytes. Substring is supported by sharing the reference to the immutable
   * underlying bytes. Concatenation is likewise supported without copying (long strings) by building
   * a tree of pieces in {@link RopeByteString}.
   *
   * <p>Like {@link String}, the contents of a {@link ByteString} can never be observed to change, not
   * even in the presence of a data race or incorrect API usage in the client code.
   *
   * @author crazybob@google.com Bob Lee
   * @author kenton@google.com Kenton Varda
   * @author carlanton@google.com Carl Haverl
   * @author martinrb@google.com Martin Buchholz
   */
  public abstract class ByteString implements Iterable<Byte>, Serializable {
  
    /**
     * When two strings to be concatenated have a combined length shorter than
     * this, we just copy their bytes on {@link #concat(ByteString)}.
     * The trade-off is copy size versus the overhead of creating tree nodes
     * in {@link RopeByteString}.
     */
    static final int CONCATENATE_BY_COPY_SIZE = 128;
  
    /**
     * When copying an InputStream into a ByteString with .readFrom(),
     * the chunks in the underlying rope start at 256 bytes, but double
     * each iteration up to 8192 bytes.
     */
    static final int MIN_READ_FROM_CHUNK_SIZE = 0x100;  // 256b
    static final int MAX_READ_FROM_CHUNK_SIZE = 0x2000;  // 8k
  
    /**
     * Empty {@code ByteString}.
     */
    public static final ByteString EMPTY = new LiteralByteString(Internal.EMPTY_BYTE_ARRAY);
  
    /**
     * An interface to efficiently copy {@code byte[]}.
     *
     * <p>One of the noticeable costs of copying a byte[] into a new array using
     * {@code System.arraycopy} is nullification of a new buffer before the copy. It has been shown
     * the Hotspot VM is capable to intrisicfy {@code Arrays.copyOfRange} operation to avoid this
     * expensive nullification and provide substantial performance gain. Unfortunately this does not
     * hold on Android runtimes and could make the copy slightly slower due to additional code in
     * the {@code Arrays.copyOfRange}. Thus we provide two different implementation for array copier
     * for Hotspot and Android runtimes.
     */
    private interface ByteArrayCopier {
      /**
       * Copies the specified range of the specified array into a new array
       */
      byte[] copyFrom(byte[] bytes, int offset, int size);
    }
  
    /** Implementation of {@code ByteArrayCopier} which uses {@link System#arraycopy}. */
    private static final class SystemByteArrayCopier implements ByteArrayCopier {
      @Override
      public byte[] copyFrom(byte[] bytes, int offset, int size) {
        byte[] copy = new byte[size];
        System.arraycopy(bytes, offset, copy, 0, size);
        return copy;
      }
    }
  
    /** Implementation of {@code ByteArrayCopier} which uses {@link Arrays#copyOfRange}. */
    private static final class ArraysByteArrayCopier implements ByteArrayCopier {
      @Override
      public byte[] copyFrom(byte[] bytes, int offset, int size) {
        return Arrays.copyOfRange(bytes, offset, offset + size);
      }
    }
  
    private static final ByteArrayCopier byteArrayCopier;
    static {
      byteArrayCopier =
          Android.isOnAndroidDevice() ? new SystemByteArrayCopier() : new ArraysByteArrayCopier();
    }
  
    /**
     * Cached hash value. Intentionally accessed via a data race, which
     * is safe because of the Java Memory Model's "no out-of-thin-air values"
     * guarantees for ints. A value of 0 implies that the hash has not been set.
     */
    private int hash = 0;
  
    // This constructor is here to prevent subclassing outside of this package,
    ByteString() {}
  
    /**
     * Gets the byte at the given index. This method should be used only for
     * random access to individual bytes. To access bytes sequentially, use the
     * {@link ByteIterator} returned by {@link #iterator()}, and call {@link
     * #substring(int, int)} first if necessary.
     *
     * @param index index of byte
     * @return the value
     * @throws IndexOutOfBoundsException {@code index < 0 or index >= size}
     */
    public abstract byte byteAt(int index);
  
    /**
     * Return a {@link ByteString.ByteIterator} over the bytes in the ByteString.
     * To avoid auto-boxing, you may get the iterator manually and call
     * {@link ByteIterator#nextByte()}.
     *
     * @return the iterator
     */
    @Override
    public final ByteIterator iterator() {
      return new ByteIterator() {
        private int position = 0;
        private final int limit = size();
  
        @Override
        public boolean hasNext() {
          return position < limit;
        }
  
        @Override
        public Byte next() {
          // Boxing calls Byte.valueOf(byte), which does not instantiate.
          return nextByte();
        }
  
        @Override
        public byte nextByte() {
          try {
            return byteAt(position++);
          } catch (IndexOutOfBoundsException e) {
            throw new NoSuchElementException(e.getMessage());
          }
        }
  
        @Override
        public void remove() {
          throw new UnsupportedOperationException();
        }
      };
    }
  
    /**
     * This interface extends {@code Iterator<Byte>}, so that we can return an
     * unboxed {@code byte}.
     */
    public interface ByteIterator extends Iterator<Byte> {
      /**
       * An alternative to {@link Iterator#next()} that returns an
       * unboxed primitive {@code byte}.
       *
       * @return the next {@code byte} in the iteration
       * @throws NoSuchElementException if the iteration has no more elements
       */
      byte nextByte();
    }
  
    /**
     * Gets the number of bytes.
     *
     * @return size in bytes
     */
    public abstract int size();
  
    /**
     * Returns {@code true} if the size is {@code 0}, {@code false} otherwise.
     *
     * @return true if this is zero bytes long
     */
    public final boolean isEmpty() {
      return size() == 0;
    }
  
    // =================================================================
    // ByteString -> substring
  
    /**
     * Return the substring from {@code beginIndex}, inclusive, to the end of the
     * string.
     *
     * @param beginIndex start at this index
     * @return substring sharing underlying data
     * @throws IndexOutOfBoundsException if {@code beginIndex < 0} or
     *     {@code beginIndex > size()}.
     */
    public final ByteString substring(int beginIndex) {
      return substring(beginIndex, size());
    }
  
    /**
     * Return the substring from {@code beginIndex}, inclusive, to {@code
     * endIndex}, exclusive.
     *
     * @param beginIndex start at this index
     * @param endIndex   the last character is the one before this index
     * @return substring sharing underlying data
     * @throws IndexOutOfBoundsException if {@code beginIndex < 0},
     *     {@code endIndex > size()}, or {@code beginIndex > endIndex}.
     */
    public abstract ByteString substring(int beginIndex, int endIndex);
  
    /**
     * Tests if this bytestring starts with the specified prefix.
     * Similar to {@link String#startsWith(String)}
     *
     * @param prefix the prefix.
     * @return <code>true</code> if the byte sequence represented by the
     *         argument is a prefix of the byte sequence represented by
     *         this string; <code>false</code> otherwise.
     */
    public final boolean startsWith(ByteString prefix) {
      return size() >= prefix.size() &&
             substring(0, prefix.size()).equals(prefix);
    }
  
    /**
     * Tests if this bytestring ends with the specified suffix.
     * Similar to {@link String#endsWith(String)}
     *
     * @param suffix the suffix.
     * @return <code>true</code> if the byte sequence represented by the
     *         argument is a suffix of the byte sequence represented by
     *         this string; <code>false</code> otherwise.
     */
    public final boolean endsWith(ByteString suffix) {
      return size() >= suffix.size() &&
          substring(size() - suffix.size()).equals(suffix);
    }
  
    // =================================================================
    // byte[] -> ByteString
  
    /**
     * Copies the given bytes into a {@code ByteString}.
     *
     * @param bytes source array
     * @param offset offset in source array
     * @param size number of bytes to copy
     * @return new {@code ByteString}
     */
    public static ByteString copyFrom(byte[] bytes, int offset, int size) {
      return new LiteralByteString(byteArrayCopier.copyFrom(bytes, offset, size));
    }
  
    /**
     * Copies the given bytes into a {@code ByteString}.
     *
     * @param bytes to copy
     * @return new {@code ByteString}
     */
    public static ByteString copyFrom(byte[] bytes) {
      return copyFrom(bytes, 0, bytes.length);
    }
  
    /**
     * Wraps the given bytes into a {@code ByteString}. Intended for internal only usage.
     */
    static ByteString wrap(ByteBuffer buffer) {
      if (buffer.hasArray()) {
        final int offset = buffer.arrayOffset();
        return ByteString.wrap(buffer.array(), offset + buffer.position(), buffer.remaining());
      } else {
        return new NioByteString(buffer);
      }
    }
  
    /**
     * Wraps the given bytes into a {@code ByteString}. Intended for internal only
     * usage to force a classload of ByteString before LiteralByteString.
     */
    static ByteString wrap(byte[] bytes) {
      // TODO(dweis): Return EMPTY when bytes are empty to reduce allocations?
      return new LiteralByteString(bytes);
    }
  
    /**
     * Wraps the given bytes into a {@code ByteString}. Intended for internal only
     * usage to force a classload of ByteString before BoundedByteString and
     * LiteralByteString.
     */
    static ByteString wrap(byte[] bytes, int offset, int length) {
      return new BoundedByteString(bytes, offset, length);
    }
  
    /**
     * Copies the next {@code size} bytes from a {@code java.nio.ByteBuffer} into
     * a {@code ByteString}.
     *
     * @param bytes source buffer
     * @param size number of bytes to copy
     * @return new {@code ByteString}
     */
    public static ByteString copyFrom(ByteBuffer bytes, int size) {
      byte[] copy = new byte[size];
      bytes.get(copy);
      return new LiteralByteString(copy);
    }
  
    /**
     * Copies the remaining bytes from a {@code java.nio.ByteBuffer} into
     * a {@code ByteString}.
     *
     * @param bytes sourceBuffer
     * @return new {@code ByteString}
     */
    public static ByteString copyFrom(ByteBuffer bytes) {
      return copyFrom(bytes, bytes.remaining());
    }
  
    /**
     * Encodes {@code text} into a sequence of bytes using the named charset
     * and returns the result as a {@code ByteString}.
     *
     * @param text source string
     * @param charsetName encoding to use
     * @return new {@code ByteString}
     * @throws UnsupportedEncodingException if the encoding isn't found
     */
    public static ByteString copyFrom(String text, String charsetName)
        throws UnsupportedEncodingException {
      return new LiteralByteString(text.getBytes(charsetName));
    }
  
    /**
     * Encodes {@code text} into a sequence of bytes using the named charset
     * and returns the result as a {@code ByteString}.
     *
     * @param text source string
     * @param charset encode using this charset
     * @return new {@code ByteString}
     */
    public static ByteString copyFrom(String text, Charset charset) {
      return new LiteralByteString(text.getBytes(charset));
    }
  
    /**
     * Encodes {@code text} into a sequence of UTF-8 bytes and returns the
     * result as a {@code ByteString}.
     *
     * @param text source string
     * @return new {@code ByteString}
     */
    public static ByteString copyFromUtf8(String text) {
      return new LiteralByteString(text.getBytes(Internal.UTF_8));
    }
  
    // =================================================================
    // InputStream -> ByteString
  
    /**
     * Completely reads the given stream's bytes into a
     * {@code ByteString}, blocking if necessary until all bytes are
     * read through to the end of the stream.
     *
     * <b>Performance notes:</b> The returned {@code ByteString} is an
     * immutable tree of byte arrays ("chunks") of the stream data.  The
     * first chunk is small, with subsequent chunks each being double
     * the size, up to 8K.
     *
     * <p>Each byte read from the input stream will be copied twice to ensure
     * that the resulting ByteString is truly immutable.
     *
     * @param streamToDrain The source stream, which is read completely
     *     but not closed.
     * @return A new {@code ByteString} which is made up of chunks of
     *     various sizes, depending on the behavior of the underlying
     *     stream.
     * @throws IOException IOException is thrown if there is a problem
     *     reading the underlying stream.
     */
    public static ByteString readFrom(InputStream streamToDrain)
        throws IOException {
      return readFrom(streamToDrain, MIN_READ_FROM_CHUNK_SIZE, MAX_READ_FROM_CHUNK_SIZE);
    }
  
    /**
     * Completely reads the given stream's bytes into a
     * {@code ByteString}, blocking if necessary until all bytes are
     * read through to the end of the stream.
     *
     * <b>Performance notes:</b> The returned {@code ByteString} is an
     * immutable tree of byte arrays ("chunks") of the stream data.  The
     * chunkSize parameter sets the size of these byte arrays.
     *
     * <p>Each byte read from the input stream will be copied twice to ensure
     * that the resulting ByteString is truly immutable.
     *
     * @param streamToDrain The source stream, which is read completely
     *     but not closed.
     * @param chunkSize The size of the chunks in which to read the
     *     stream.
     * @return A new {@code ByteString} which is made up of chunks of
     *     the given size.
     * @throws IOException IOException is thrown if there is a problem
     *     reading the underlying stream.
     */
    public static ByteString readFrom(InputStream streamToDrain, int chunkSize)
        throws IOException {
      return readFrom(streamToDrain, chunkSize, chunkSize);
    }
  
    // Helper method that takes the chunk size range as a parameter.
    public static ByteString readFrom(InputStream streamToDrain, int minChunkSize,
        int maxChunkSize) throws IOException {
      Collection<ByteString> results = new ArrayList<ByteString>();
  
      // copy the inbound bytes into a list of chunks; the chunk size
      // grows exponentially to support both short and long streams.
      int chunkSize = minChunkSize;
      while (true) {
        ByteString chunk = readChunk(streamToDrain, chunkSize);
        if (chunk == null) {
          break;
        }
        results.add(chunk);
        chunkSize = Math.min(chunkSize * 2, maxChunkSize);
      }
  
      return ByteString.copyFrom(results);
    }
  
    /**
     * Blocks until a chunk of the given size can be made from the
     * stream, or EOF is reached.  Calls read() repeatedly in case the
     * given stream implementation doesn't completely fill the given
     * buffer in one read() call.
     *
     * @return A chunk of the desired size, or else a chunk as large as
     * was available when end of stream was reached. Returns null if the
     * given stream had no more data in it.
     */
    private static ByteString readChunk(InputStream in, final int chunkSize)
        throws IOException {
        final byte[] buf = new byte[chunkSize];
        int bytesRead = 0;
        while (bytesRead < chunkSize) {
          final int count = in.read(buf, bytesRead, chunkSize - bytesRead);
          if (count == -1) {
            break;
          }
          bytesRead += count;
        }
  
        if (bytesRead == 0) {
          return null;
        }
  
        // Always make a copy since InputStream could steal a reference to buf.
        return ByteString.copyFrom(buf, 0, bytesRead);
    }
  
    // =================================================================
    // Multiple ByteStrings -> One ByteString
  
    /**
     * Concatenate the given {@code ByteString} to this one. Short concatenations,
     * of total size smaller than {@link ByteString#CONCATENATE_BY_COPY_SIZE}, are
     * produced by copying the underlying bytes (as per Rope.java, <a
     * href="http://www.cs.ubc.ca/local/reading/proceedings/spe91-95/spe/vol25/issue12/spe986.pdf">
     * BAP95 </a>. In general, the concatenate involves no copying.
     *
     * @param other string to concatenate
     * @return a new {@code ByteString} instance
     */
    public final ByteString concat(ByteString other) {
      if (Integer.MAX_VALUE - size() < other.size()) {
        throw new IllegalArgumentException("ByteString would be too long: " +
            size() + "+" + other.size());
      }
  
      return RopeByteString.concatenate(this, other);
    }
  
    /**
     * Concatenates all byte strings in the iterable and returns the result.
     * This is designed to run in O(list size), not O(total bytes).
     *
     * <p>The returned {@code ByteString} is not necessarily a unique object.
     * If the list is empty, the returned object is the singleton empty
     * {@code ByteString}.  If the list has only one element, that
     * {@code ByteString} will be returned without copying.
     *
     * @param byteStrings strings to be concatenated
     * @return new {@code ByteString}
     */
    public static ByteString copyFrom(Iterable<ByteString> byteStrings) {
      // Determine the size;
      final int size;
      if (!(byteStrings instanceof Collection)) {
        int tempSize = 0;
        for (Iterator<ByteString> iter = byteStrings.iterator(); iter.hasNext();
            iter.next(), ++tempSize) {
        }
        size = tempSize;
      } else {
        size = ((Collection<ByteString>) byteStrings).size();
      }
  
      if (size == 0) {
        return EMPTY;
      }
  
      return balancedConcat(byteStrings.iterator(), size);
    }
  
    // Internal function used by copyFrom(Iterable<ByteString>).
    // Create a balanced concatenation of the next "length" elements from the
    // iterable.
    private static ByteString balancedConcat(Iterator<ByteString> iterator, int length) {
      if (length < 1) {
        throw new IllegalArgumentException(String.format("length (%s) must be >= 1", length));
      }
      ByteString result;
      if (length == 1) {
        result = iterator.next();
      } else {
        int halfLength = length >>> 1;
        ByteString left = balancedConcat(iterator, halfLength);
        ByteString right = balancedConcat(iterator, length - halfLength);
        result = left.concat(right);
      }
      return result;
    }
  
    // =================================================================
    // ByteString -> byte[]
  
    /**
     * Copies bytes into a buffer at the given offset.
     *
     * @param target buffer to copy into
     * @param offset in the target buffer
     * @throws IndexOutOfBoundsException if the offset is negative or too large
     */
    public void copyTo(byte[] target, int offset) {
      copyTo(target, 0, offset, size());
    }
  
    /**
     * Copies bytes into a buffer.
     *
     * @param target       buffer to copy into
     * @param sourceOffset offset within these bytes
     * @param targetOffset offset within the target buffer
     * @param numberToCopy number of bytes to copy
     * @throws IndexOutOfBoundsException if an offset or size is negative or too
     *     large
     */
    public final void copyTo(byte[] target, int sourceOffset, int targetOffset,
        int numberToCopy) {
      checkRange(sourceOffset, sourceOffset + numberToCopy, size());
      checkRange(targetOffset, targetOffset + numberToCopy, target.length);
      if (numberToCopy > 0) {
        copyToInternal(target, sourceOffset, targetOffset, numberToCopy);
      }
    }
  
    /**
     * Internal (package private) implementation of
     * {@link #copyTo(byte[],int,int,int)}.
     * It assumes that all error checking has already been performed and that
     * {@code numberToCopy > 0}.
     */
    protected abstract void copyToInternal(byte[] target, int sourceOffset,
        int targetOffset, int numberToCopy);
  
    /**
     * Copies bytes into a ByteBuffer.
     *
     * @param target ByteBuffer to copy into.
     * @throws java.nio.ReadOnlyBufferException if the {@code target} is read-only
     * @throws java.nio.BufferOverflowException if the {@code target}'s
     *     remaining() space is not large enough to hold the data.
     */
    public abstract void copyTo(ByteBuffer target);
  
    /**
     * Copies bytes to a {@code byte[]}.
     *
     * @return copied bytes
     */
    public final byte[] toByteArray() {
      final int size = size();
      if (size == 0) {
        return Internal.EMPTY_BYTE_ARRAY;
      }
      byte[] result = new byte[size];
      copyToInternal(result, 0, 0, size);
      return result;
    }
  
    /**
     * Writes a copy of the contents of this byte string to the specified output stream argument.
     *
     * @param  out  the output stream to which to write the data.
     * @throws IOException  if an I/O error occurs.
     */
    public abstract void writeTo(OutputStream out) throws IOException;
  
    /**
     * Writes a specified part of this byte string to an output stream.
     *
     * @param  out  the output stream to which to write the data.
     * @param  sourceOffset offset within these bytes
     * @param  numberToWrite number of bytes to write
     * @throws IOException  if an I/O error occurs.
     * @throws IndexOutOfBoundsException if an offset or size is negative or too large
     */
    final void writeTo(OutputStream out, int sourceOffset, int numberToWrite)
        throws IOException {
      checkRange(sourceOffset, sourceOffset + numberToWrite, size());
      if (numberToWrite > 0) {
        writeToInternal(out, sourceOffset, numberToWrite);
      }
    }
  
    /**
     * Internal version of {@link #writeTo(OutputStream,int,int)} that assumes
     * all error checking has already been done.
     */
    abstract void writeToInternal(OutputStream out, int sourceOffset, int numberToWrite)
        throws IOException;
  
    /**
     * Writes this {@link ByteString} to the provided {@link ByteOutput}. Calling
     * this method may result in multiple operations on the target {@link ByteOutput}.
     *
     * <p>This method may expose internal backing buffers of the {@link ByteString} to the {@link
     * ByteOutput} in order to avoid additional copying overhead. It would be possible for a malicious
     * {@link ByteOutput} to corrupt the {@link ByteString}. Use with caution!
     *
     * @param  byteOutput  the output target to receive the bytes
     * @throws IOException  if an I/O error occurs
     * @see UnsafeByteOperations#unsafeWriteTo(ByteString, ByteOutput)
     */
    abstract void writeTo(ByteOutput byteOutput) throws IOException;
  
  
    /**
     * Constructs a read-only {@code java.nio.ByteBuffer} whose content
     * is equal to the contents of this byte string.
     * The result uses the same backing array as the byte string, if possible.
     *
     * @return wrapped bytes
     */
    public abstract ByteBuffer asReadOnlyByteBuffer();
  
    /**
     * Constructs a list of read-only {@code java.nio.ByteBuffer} objects
     * such that the concatenation of their contents is equal to the contents
     * of this byte string.  The result uses the same backing arrays as the
     * byte string.
     * <p>
     * By returning a list, implementations of this method may be able to avoid
     * copying even when there are multiple backing arrays.
     *
     * @return a list of wrapped bytes
     */
    public abstract List<ByteBuffer> asReadOnlyByteBufferList();
  
    /**
     * Constructs a new {@code String} by decoding the bytes using the
     * specified charset.
     *
     * @param charsetName encode using this charset
     * @return new string
     * @throws UnsupportedEncodingException if charset isn't recognized
     */
    public final String toString(String charsetName)
        throws UnsupportedEncodingException {
      try {
        return toString(Charset.forName(charsetName));
      } catch (UnsupportedCharsetException e) {
        UnsupportedEncodingException exception = new UnsupportedEncodingException(charsetName);
        exception.initCause(e);
        throw exception;
      }
    }
  
    /**
     * Constructs a new {@code String} by decoding the bytes using the
     * specified charset. Returns the same empty String if empty.
     *
     * @param charset encode using this charset
     * @return new string
     */
    public final String toString(Charset charset) {
      return size() == 0 ? "" : toStringInternal(charset);
    }
  
    /**
     * Constructs a new {@code String} by decoding the bytes using the
     * specified charset.
     *
     * @param charset encode using this charset
     * @return new string
     */
    protected abstract String toStringInternal(Charset charset);
  
    // =================================================================
    // UTF-8 decoding
  
    /**
     * Constructs a new {@code String} by decoding the bytes as UTF-8.
     *
     * @return new string using UTF-8 encoding
     */
    public final String toStringUtf8() {
      return toString(Internal.UTF_8);
    }
  
    /**
     * Tells whether this {@code ByteString} represents a well-formed UTF-8
     * byte sequence, such that the original bytes can be converted to a
     * String object and then round tripped back to bytes without loss.
     *
     * <p>More precisely, returns {@code true} whenever: <pre> {@code
     * Arrays.equals(byteString.toByteArray(),
     *     new String(byteString.toByteArray(), "UTF-8").getBytes("UTF-8"))
     * }</pre>
     *
     * <p>This method returns {@code false} for "overlong" byte sequences,
     * as well as for 3-byte sequences that would map to a surrogate
     * character, in accordance with the restricted definition of UTF-8
     * introduced in Unicode 3.1.  Note that the UTF-8 decoder included in
     * Oracle's JDK has been modified to also reject "overlong" byte
     * sequences, but (as of 2011) still accepts 3-byte surrogate
     * character byte sequences.
     *
     * <p>See the Unicode Standard,<br>
     * Table 3-6. <em>UTF-8 Bit Distribution</em>,<br>
     * Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
     *
     * @return whether the bytes in this {@code ByteString} are a
     * well-formed UTF-8 byte sequence
     */
    public abstract boolean isValidUtf8();
  
    /**
     * Tells whether the given byte sequence is a well-formed, malformed, or
     * incomplete UTF-8 byte sequence.  This method accepts and returns a partial
     * state result, allowing the bytes for a complete UTF-8 byte sequence to be
     * composed from multiple {@code ByteString} segments.
     *
     * @param state either {@code 0} (if this is the initial decoding operation)
     *     or the value returned from a call to a partial decoding method for the
     *     previous bytes
     * @param offset offset of the first byte to check
     * @param length number of bytes to check
     *
     * @return {@code -1} if the partial byte sequence is definitely malformed,
     * {@code 0} if it is well-formed (no additional input needed), or, if the
     * byte sequence is "incomplete", i.e. apparently terminated in the middle of
     * a character, an opaque integer "state" value containing enough information
     * to decode the character when passed to a subsequent invocation of a
     * partial decoding method.
     */
    protected abstract int partialIsValidUtf8(int state, int offset, int length);
  
    // =================================================================
    // equals() and hashCode()
  
    @Override
    public abstract boolean equals(Object o);
  
    /**
     * Base class for leaf {@link ByteString}s (i.e. non-ropes).
     */
    abstract static class LeafByteString extends ByteString {
      @Override
      protected final int getTreeDepth() {
        return 0;
      }
  
      @Override
      protected final boolean isBalanced() {
        return true;
      }
  
  
      /**
       * Check equality of the substring of given length of this object starting at
       * zero with another {@code ByteString} substring starting at offset.
       *
       * @param other  what to compare a substring in
       * @param offset offset into other
       * @param length number of bytes to compare
       * @return true for equality of substrings, else false.
       */
      abstract boolean equalsRange(ByteString other, int offset, int length);
    }
  
    /**
     * Compute the hashCode using the traditional algorithm from {@link
     * ByteString}.
     *
     * @return hashCode value
     */
    @Override
    public final int hashCode() {
      int h = hash;
  
      if (h == 0) {
        int size = size();
        h = partialHash(size, 0, size);
        if (h == 0) {
          h = 1;
        }
        hash = h;
      }
      return h;
    }
  
    // =================================================================
    // Input stream
  
    /**
     * Creates an {@code InputStream} which can be used to read the bytes.
     * <p>
     * The {@link InputStream} returned by this method is guaranteed to be
     * completely non-blocking.  The method {@link InputStream#available()}
     * returns the number of bytes remaining in the stream. The methods
     * {@link InputStream#read(byte[])}, {@link InputStream#read(byte[],int,int)}
     * and {@link InputStream#skip(long)} will read/skip as many bytes as are
     * available.  The method {@link InputStream#markSupported()} returns
     * {@code true}.
     * <p>
     * The methods in the returned {@link InputStream} might <b>not</b> be
     * thread safe.
     *
     * @return an input stream that returns the bytes of this byte string.
     */
    public abstract InputStream newInput();
  
    /**
     * Creates a {@link CodedInputStream} which can be used to read the bytes.
     * Using this is often more efficient than creating a {@link CodedInputStream}
     * that wraps the result of {@link #newInput()}.
     *
     * @return stream based on wrapped data
     */
    public abstract CodedInputStream newCodedInput();
  
    // =================================================================
    // Output stream
  
    /**
     * Creates a new {@link Output} with the given initial capacity. Call {@link
     * Output#toByteString()} to create the {@code ByteString} instance.
     * <p>
     * A {@link ByteString.Output} offers the same functionality as a
     * {@link ByteArrayOutputStream}, except that it returns a {@link ByteString}
     * rather than a {@code byte} array.
     *
     * @param initialCapacity estimate of number of bytes to be written
     * @return {@code OutputStream} for building a {@code ByteString}
     */
    public static Output newOutput(int initialCapacity) {
      return new Output(initialCapacity);
    }
  
    /**
     * Creates a new {@link Output}. Call {@link Output#toByteString()} to create
     * the {@code ByteString} instance.
     * <p>
     * A {@link ByteString.Output} offers the same functionality as a
     * {@link ByteArrayOutputStream}, except that it returns a {@link ByteString}
     * rather than a {@code byte array}.
     *
     * @return {@code OutputStream} for building a {@code ByteString}
     */
    public static Output newOutput() {
      return new Output(CONCATENATE_BY_COPY_SIZE);
    }
  
    /**
     * Outputs to a {@code ByteString} instance. Call {@link #toByteString()} to
     * create the {@code ByteString} instance.
     */
    public static final class Output extends OutputStream {
      // Implementation note.
      // The public methods of this class must be synchronized.  ByteStrings
      // are guaranteed to be immutable.  Without some sort of locking, it could
      // be possible for one thread to call toByteSring(), while another thread
      // is still modifying the underlying byte array.
  
      private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
      // argument passed by user, indicating initial capacity.
      private final int initialCapacity;
      // ByteStrings to be concatenated to create the result
      private final ArrayList<ByteString> flushedBuffers;
      // Total number of bytes in the ByteStrings of flushedBuffers
      private int flushedBuffersTotalBytes;
      // Current buffer to which we are writing
      private byte[] buffer;
      // Location in buffer[] to which we write the next byte.
      private int bufferPos;
  
      /**
       * Creates a new ByteString output stream with the specified
       * initial capacity.
       *
       * @param initialCapacity  the initial capacity of the output stream.
       */
      Output(int initialCapacity) {
        if (initialCapacity < 0) {
          throw new IllegalArgumentException("Buffer size < 0");
        }
        this.initialCapacity = initialCapacity;
        this.flushedBuffers = new ArrayList<ByteString>();
        this.buffer = new byte[initialCapacity];
      }
  
      @Override
      public synchronized void write(int b) {
        if (bufferPos == buffer.length) {
          flushFullBuffer(1);
        }
        buffer[bufferPos++] = (byte)b;
      }
  
      @Override
      public synchronized void write(byte[] b, int offset, int length)  {
        if (length <= buffer.length - bufferPos) {
          // The bytes can fit into the current buffer.
          System.arraycopy(b, offset, buffer, bufferPos, length);
          bufferPos += length;
        } else {
          // Use up the current buffer
          int copySize  = buffer.length - bufferPos;
          System.arraycopy(b, offset, buffer, bufferPos, copySize);
          offset += copySize;
          length -= copySize;
          // Flush the buffer, and get a new buffer at least big enough to cover
          // what we still need to output
          flushFullBuffer(length);
          System.arraycopy(b, offset, buffer, 0 /* count */, length);
          bufferPos = length;
        }
      }
  
      /**
       * Creates a byte string. Its size is the current size of this output
       * stream and its output has been copied to it.
       *
       * @return  the current contents of this output stream, as a byte string.
       */
      public synchronized ByteString toByteString() {
        flushLastBuffer();
        return ByteString.copyFrom(flushedBuffers);
      }
  
      /**
       * Implement java.util.Arrays.copyOf() for jdk 1.5.
       */
      private byte[] copyArray(byte[] buffer, int length) {
        byte[] result = new byte[length];
        System.arraycopy(buffer, 0, result, 0, Math.min(buffer.length, length));
        return result;
      }
  
      /**
       * Writes the complete contents of this byte array output stream to
       * the specified output stream argument.
       *
       * @param out the output stream to which to write the data.
       * @throws IOException  if an I/O error occurs.
       */
      public void writeTo(OutputStream out) throws IOException {
        ByteString[] cachedFlushBuffers;
        byte[] cachedBuffer;
        int cachedBufferPos;
        synchronized (this) {
          // Copy the information we need into local variables so as to hold
          // the lock for as short a time as possible.
          cachedFlushBuffers =
              flushedBuffers.toArray(new ByteString[flushedBuffers.size()]);
          cachedBuffer = buffer;
          cachedBufferPos = bufferPos;
        }
        for (ByteString byteString : cachedFlushBuffers) {
          byteString.writeTo(out);
        }
  
        out.write(copyArray(cachedBuffer, cachedBufferPos));
      }
  
      /**
       * Returns the current size of the output stream.
       *
       * @return  the current size of the output stream
       */
      public synchronized int size() {
        return flushedBuffersTotalBytes + bufferPos;
      }
  
      /**
       * Resets this stream, so that all currently accumulated output in the
       * output stream is discarded. The output stream can be used again,
       * reusing the already allocated buffer space.
       */
      public synchronized void reset() {
        flushedBuffers.clear();
        flushedBuffersTotalBytes = 0;
        bufferPos = 0;
      }
  
      @Override
      public String toString() {
        return String.format("<ByteString.Output@%s size=%d>",
            Integer.toHexString(System.identityHashCode(this)), size());
      }
  
      /**
       * Internal function used by writers.  The current buffer is full, and the
       * writer needs a new buffer whose size is at least the specified minimum
       * size.
       */
      private void flushFullBuffer(int minSize)  {
        flushedBuffers.add(new LiteralByteString(buffer));
        flushedBuffersTotalBytes += buffer.length;
        // We want to increase our total capacity by 50%, but as a minimum,
        // the new buffer should also at least be >= minSize and
        // >= initial Capacity.
        int newSize = Math.max(initialCapacity,
            Math.max(minSize, flushedBuffersTotalBytes >>> 1));
        buffer = new byte[newSize];
        bufferPos = 0;
      }
  
      /**
       * Internal function used by {@link #toByteString()}. The current buffer may
       * or may not be full, but it needs to be flushed.
       */
      private void flushLastBuffer()  {
        if (bufferPos < buffer.length) {
          if (bufferPos > 0) {
            byte[] bufferCopy = copyArray(buffer, bufferPos);
            flushedBuffers.add(new LiteralByteString(bufferCopy));
          }
          // We reuse this buffer for further writes.
        } else {
          // Buffer is completely full.  Huzzah.
          flushedBuffers.add(new LiteralByteString(buffer));
          // 99% of the time, we're not going to use this OutputStream again.
          // We set buffer to an empty byte stream so that we're handling this
          // case without wasting space.  In the rare case that more writes
          // *do* occur, this empty buffer will be flushed and an appropriately
          // sized new buffer will be created.
          buffer = EMPTY_BYTE_ARRAY;
        }
        flushedBuffersTotalBytes += bufferPos;
        bufferPos = 0;
      }
    }
  
    /**
     * Constructs a new {@code ByteString} builder, which allows you to
     * efficiently construct a {@code ByteString} by writing to a {@link
     * CodedOutputStream}. Using this is much more efficient than calling {@code
     * newOutput()} and wrapping that in a {@code CodedOutputStream}.
     *
     * <p>This is package-private because it's a somewhat confusing interface.
     * Users can call {@link Message#toByteString()} instead of calling this
     * directly.
     *
     * @param size The target byte size of the {@code ByteString}.  You must write
     *     exactly this many bytes before building the result.
     * @return the builder
     */
    static CodedBuilder newCodedBuilder(int size) {
      return new CodedBuilder(size);
    }
  
    /** See {@link ByteString#newCodedBuilder(int)}. */
    static final class CodedBuilder {
      private final CodedOutputStream output;
      private final byte[] buffer;
  
      private CodedBuilder(int size) {
        buffer = new byte[size];
        output = CodedOutputStream.newInstance(buffer);
      }
  
      public ByteString build() {
        output.checkNoSpaceLeft();
  
        // We can be confident that the CodedOutputStream will not modify the
        // underlying bytes anymore because it already wrote all of them.  So,
        // no need to make a copy.
        return new LiteralByteString(buffer);
      }
  
      public CodedOutputStream getCodedOutput() {
        return output;
      }
    }
  
    // =================================================================
    // Methods {@link RopeByteString} needs on instances, which aren't part of the
    // public API.
  
    /**
     * Return the depth of the tree representing this {@code ByteString}, if any,
     * whose root is this node. If this is a leaf node, return 0.
     *
     * @return tree depth or zero
     */
    protected abstract int getTreeDepth();
  
    /**
     * Return {@code true} if this ByteString is literal (a leaf node) or a
     * flat-enough tree in the sense of {@link RopeByteString}.
     *
     * @return true if the tree is flat enough
     */
    protected abstract boolean isBalanced();
  
    /**
     * Return the cached hash code if available.
     *
     * @return value of cached hash code or 0 if not computed yet
     */
    protected final int peekCachedHashCode() {
      return hash;
    }
  
    /**
     * Compute the hash across the value bytes starting with the given hash, and
     * return the result.  This is used to compute the hash across strings
     * represented as a set of pieces by allowing the hash computation to be
     * continued from piece to piece.
     *
     * @param h starting hash value
     * @param offset offset into this value to start looking at data values
     * @param length number of data values to include in the hash computation
     * @return ending hash value
     */
    protected abstract int partialHash(int h, int offset, int length);
  
    /**
     * Checks that the given index falls within the specified array size.
     *
     * @param index the index position to be tested
     * @param size the length of the array
     * @throws IndexOutOfBoundsException if the index does not fall within the array.
     */
    static void checkIndex(int index, int size) {
      if ((index | (size - (index + 1))) < 0) {
        if (index < 0) {
          throw new ArrayIndexOutOfBoundsException("Index < 0: " + index);
        }
        throw new ArrayIndexOutOfBoundsException("Index > length: " + index + ", " + size);
      }
    }
  
    /**
     * Checks that the given range falls within the bounds of an array
     *
     * @param startIndex the start index of the range (inclusive)
     * @param endIndex the end index of the range (exclusive)
     * @param size the size of the array.
     * @return the length of the range.
     * @throws IndexOutOfBoundsException some or all of the range falls outside of the array.
     */
    static int checkRange(int startIndex, int endIndex, int size) {
      final int length = endIndex - startIndex;
      if ((startIndex | endIndex | length | (size - endIndex)) < 0) {
        if (startIndex < 0) {
          throw new IndexOutOfBoundsException("Beginning index: " + startIndex + " < 0");
        }
        if (endIndex < startIndex) {
          throw new IndexOutOfBoundsException(
              "Beginning index larger than ending index: " + startIndex + ", " + endIndex);
        }
        // endIndex >= size
        throw new IndexOutOfBoundsException("End index: " + endIndex + " >= " + size);
      }
      return length;
    }
  
    @Override
    public final String toString() {
      return String.format("<ByteString@%s size=%d>",
          Integer.toHexString(System.identityHashCode(this)), size());
    }
  
    /**
     * This class implements a {@link com.google.protobuf.ByteString} backed by a
     * single array of bytes, contiguous in memory. It supports substring by
     * pointing to only a sub-range of the underlying byte array, meaning that a
     * substring will reference the full byte-array of the string it's made from,
     * exactly as with {@link String}.
     *
     * @author carlanton@google.com (Carl Haverl)
     */
    // Keep this class private to avoid deadlocks in classloading across threads as ByteString's
    // static initializer loads LiteralByteString and another thread loads LiteralByteString.
    private static class LiteralByteString extends ByteString.LeafByteString {
      private static final long serialVersionUID = 1L;
  
      protected final byte[] bytes;
  
      /**
       * Creates a {@code LiteralByteString} backed by the given array, without
       * copying.
       *
       * @param bytes array to wrap
       */
      LiteralByteString(byte[] bytes) {
        this.bytes = bytes;
      }
  
      @Override
      public byte byteAt(int index) {
        // Unlike most methods in this class, this one is a direct implementation
        // ignoring the potential offset because we need to do range-checking in the
        // substring case anyway.
        return bytes[index];
      }
  
      @Override
      public int size() {
        return bytes.length;
      }
  
      // =================================================================
      // ByteString -> substring
  
      @Override
      public final ByteString substring(int beginIndex, int endIndex) {
        final int length = checkRange(beginIndex, endIndex, size());
  
        if (length == 0) {
          return ByteString.EMPTY;
        }
  
        return new BoundedByteString(bytes, getOffsetIntoBytes() + beginIndex, length);
      }
  
      // =================================================================
      // ByteString -> byte[]
  
      @Override
      protected void copyToInternal(
          byte[] target, int sourceOffset, int targetOffset, int numberToCopy) {
        // Optimized form, not for subclasses, since we don't call
        // getOffsetIntoBytes() or check the 'numberToCopy' parameter.
        // TODO(nathanmittler): Is not calling getOffsetIntoBytes really saving that much?
        System.arraycopy(bytes, sourceOffset, target, targetOffset, numberToCopy);
      }
  
      @Override
      public final void copyTo(ByteBuffer target) {
        target.put(bytes, getOffsetIntoBytes(), size()); // Copies bytes
      }
  
      @Override
      public final ByteBuffer asReadOnlyByteBuffer() {
        return ByteBuffer.wrap(bytes, getOffsetIntoBytes(), size()).asReadOnlyBuffer();
      }
  
      @Override
      public final List<ByteBuffer> asReadOnlyByteBufferList() {
        return Collections.singletonList(asReadOnlyByteBuffer());
      }
  
      @Override
      public final void writeTo(OutputStream outputStream) throws IOException {
        outputStream.write(toByteArray());
      }
  
      @Override
      final void writeToInternal(OutputStream outputStream, int sourceOffset, int numberToWrite)
          throws IOException {
        outputStream.write(bytes, getOffsetIntoBytes() + sourceOffset, numberToWrite);
      }
  
      @Override
      final void writeTo(ByteOutput output) throws IOException {
        output.writeLazy(bytes, getOffsetIntoBytes(), size());
      }
  
      @Override
      protected final String toStringInternal(Charset charset) {
        return new String(bytes, getOffsetIntoBytes(), size(), charset);
      }
  
      // =================================================================
      // UTF-8 decoding
  
      @Override
      public final boolean isValidUtf8() {
        int offset = getOffsetIntoBytes();
        return Utf8.isValidUtf8(bytes, offset, offset + size());
      }
  
      @Override
      protected final int partialIsValidUtf8(int state, int offset, int length) {
        int index = getOffsetIntoBytes() + offset;
        return Utf8.partialIsValidUtf8(state, bytes, index, index + length);
      }
  
      // =================================================================
      // equals() and hashCode()
  
      @Override
      public final boolean equals(Object other) {
        if (other == this) {
          return true;
        }
        if (!(other instanceof ByteString)) {
          return false;
        }
  
        if (size() != ((ByteString) other).size()) {
          return false;
        }
        if (size() == 0) {
          return true;
        }
  
        if (other instanceof LiteralByteString) {
          LiteralByteString otherAsLiteral = (LiteralByteString) other;
          // If we know the hash codes and they are not equal, we know the byte
          // strings are not equal.
          int thisHash = peekCachedHashCode();
          int thatHash = otherAsLiteral.peekCachedHashCode();
          if (thisHash != 0 && thatHash != 0 && thisHash != thatHash) {
            return false;
          }
  
          return equalsRange((LiteralByteString) other, 0, size());
        } else {
          // RopeByteString and NioByteString.
          return other.equals(this);
        }
      }
  
      /**
       * Check equality of the substring of given length of this object starting at
       * zero with another {@code LiteralByteString} substring starting at offset.
       *
       * @param other  what to compare a substring in
       * @param offset offset into other
       * @param length number of bytes to compare
       * @return true for equality of substrings, else false.
       */
      @Override
      final boolean equalsRange(ByteString other, int offset, int length) {
        if (length > other.size()) {
          throw new IllegalArgumentException("Length too large: " + length + size());
        }
        if (offset + length > other.size()) {
          throw new IllegalArgumentException(
              "Ran off end of other: " + offset + ", " + length + ", " + other.size());
        }
  
        if (other instanceof LiteralByteString) {
          LiteralByteString lbsOther = (LiteralByteString) other;
          byte[] thisBytes = bytes;
          byte[] otherBytes = lbsOther.bytes;
          int thisLimit = getOffsetIntoBytes() + length;
          for (
              int thisIndex = getOffsetIntoBytes(),
                  otherIndex = lbsOther.getOffsetIntoBytes() + offset;
              (thisIndex < thisLimit); ++thisIndex, ++otherIndex) {
            if (thisBytes[thisIndex] != otherBytes[otherIndex]) {
              return false;
            }
          }
          return true;
        }
  
        return other.substring(offset, offset + length).equals(substring(0, length));
      }
  
      @Override
      protected final int partialHash(int h, int offset, int length) {
        return Internal.partialHash(h, bytes, getOffsetIntoBytes() + offset, length);
      }
  
      // =================================================================
      // Input stream
  
      @Override
      public final InputStream newInput() {
        return new ByteArrayInputStream(bytes, getOffsetIntoBytes(), size()); // No copy
      }
  
      @Override
      public final CodedInputStream newCodedInput() {
        // We trust CodedInputStream not to modify the bytes, or to give anyone
        // else access to them.
        return CodedInputStream.newInstance(
            bytes, getOffsetIntoBytes(), size(), true /* bufferIsImmutable */);
      }
  
      // =================================================================
      // Internal methods
  
      /**
       * Offset into {@code bytes[]} to use, non-zero for substrings.
       *
       * @return always 0 for this class
       */
      protected int getOffsetIntoBytes() {
        return 0;
      }
    }
  
    /**
     * This class is used to represent the substring of a {@link ByteString} over a
     * single byte array. In terms of the public API of {@link ByteString}, you end
     * up here by calling {@link ByteString#copyFrom(byte[])} followed by {@link
     * ByteString#substring(int, int)}.
     *
     * <p>This class contains most of the overhead involved in creating a substring
     * from a {@link LiteralByteString}.  The overhead involves some range-checking
     * and two extra fields.
     *
     * @author carlanton@google.com (Carl Haverl)
     */
    // Keep this class private to avoid deadlocks in classloading across threads as ByteString's
    // static initializer loads LiteralByteString and another thread loads BoundedByteString.
    private static final class BoundedByteString extends LiteralByteString {
  
      private final int bytesOffset;
      private final int bytesLength;
  
      /**
       * Creates a {@code BoundedByteString} backed by the sub-range of given array,
       * without copying.
       *
       * @param bytes  array to wrap
       * @param offset index to first byte to use in bytes
       * @param length number of bytes to use from bytes
       * @throws IllegalArgumentException if {@code offset < 0}, {@code length < 0},
       *                                  or if {@code offset + length >
       *                                  bytes.length}.
       */
      BoundedByteString(byte[] bytes, int offset, int length) {
        super(bytes);
        checkRange(offset, offset + length, bytes.length);
  
        this.bytesOffset = offset;
        this.bytesLength = length;
      }
  
      /**
       * Gets the byte at the given index.
       * Throws {@link ArrayIndexOutOfBoundsException}
       * for backwards-compatibility reasons although it would more properly be
       * {@link IndexOutOfBoundsException}.
       *
       * @param index index of byte
       * @return the value
       * @throws ArrayIndexOutOfBoundsException {@code index} is < 0 or >= size
       */
      @Override
      public byte byteAt(int index) {
        // We must check the index ourselves as we cannot rely on Java array index
        // checking for substrings.
        checkIndex(index, size());
        return bytes[bytesOffset + index];
      }
  
      @Override
      public int size() {
        return bytesLength;
      }
  
      @Override
      protected int getOffsetIntoBytes() {
        return bytesOffset;
      }
  
      // =================================================================
      // ByteString -> byte[]
  
      @Override
      protected void copyToInternal(byte[] target, int sourceOffset, int targetOffset,
          int numberToCopy) {
        System.arraycopy(bytes, getOffsetIntoBytes() + sourceOffset, target,
            targetOffset, numberToCopy);
      }
  
      // =================================================================
      // Serializable
  
      private static final long serialVersionUID = 1L;
  
      Object writeReplace() {
        return ByteString.wrap(toByteArray());
      }
  
      private void readObject(@SuppressWarnings("unused") ObjectInputStream in) throws IOException {
        throw new InvalidObjectException(
            "BoundedByteStream instances are not to be serialized directly");
      }
    }
  }
  